fiction - What does Show don't Tell actually mean

I am asking this question because I think we need a precise definition of what Show Don't Tell means if we are to decide if it is good advice or bad, or if it is a valid suggestion for certain passages but not a general rule for a whole book.

Orson Scott Card was a particular critic of Show Don't Tell

OSC Replies: You said: "I made it a point throughout the novel to not tell motivations, but try to show them."

And you did this because ... of those morons who told you "show don't tell"?

Because motivation is unshowable. It must be told. (In fact, most things must be told.) The advice "show don't tell" is applicable in only a few situations -- most times, most things, you tell-don't-show. I get so impatient with this idiotic advice that has been plaguing writers for generations.

But in this discussion it is suggested that reporting of motivations is allowed in Show Don't Tell, which provokes the question: what is in and what is out in Show Don't Tell. Because if it is good advice or bad, we can't expect people to follow it if it is not well defined.